The present invention relates to a semiconductor device and a manufacturing method thereof, and particularly to a technique effective if applied to a semiconductor device equipped with a Schottky barrier diode.
The development of a liquid crystal display (LCD) or the like widely already in actual use as a display device is being carried out with the objective of making further high definition, life extension and the like. A semiconductor device called “LCD driving integrated circuit (driver IC: Integrated Circuit or called simply “driver”)” is used for control of the operation of the LCD.
In a driving integrated circuit used at a location close to a power supply as well as an LCD driver, a backward current introduced into a main apparatus due to voltage inversion at the supply of power, for example can lead to a so-called latch-up phenomenon that causes abnormal generation of heat at a parasitic element or the like in particular. As a device for preventing such latch-up phenomenon, a diode that rectifies the backward current flowing into each of principal parts of various drivers has been built in each of the various drivers. In particular, a Schottky barrier diode (SBD or called simply “Schottky Diode”) is applied to an LCD driver discussed by the present inventors et al. The basic principle of operation of the Schottky barrier diode and its electrical characteristics, which are required to explain its reason, will be descried below in brief.
The Schottky barrier diode comprises a junction of a metal material and a semiconductor material. Considering in particular a junction where there is a difference between the work function of the metal material and the electron affinity of the semiconductor material, the above difference in energy is held at a junction surface in a state of equilibrium, and they are bonded to each other in such a manner that both are made identical in Fermi level inside the material. Thus, a potential barrier equivalent to the original difference between the work function and the electron affinity occurs at the junction surface. Particularly when the height of the barrier is sufficiently larger than thermal energy, the transportation of such carriers that come and go between the metal/semiconductor materials is inhibited thereby. Such a barrier is called “Schottky barrier” in particular. The junction of the metal and semiconductor materials having the physical properties that can yield the Schottky barrier is described below as a Schottky junction.
Here, when an electric field is applied to the Schottky junction, a potential distribution changes on the semiconductor side. That is, although the height per se of the Schottky barrier corresponding to a potential discontinuous quantity at a junction boundary remains unchanged, the height of the Schottky barrier as viewed from a majority carrier on the semiconductor side changes. Thus, the majority carrier transported to the metal side beyond the Schottky barrier only by thermal energy appears depending on field conditions, and hence the current equivalent to this flows (forward characteristic). On the other hand, the height of the Schottky barrier as viewed from the carriers remains unchanged on the metal side that does not cause a large change in potential distribution even when the electric field is applied. That is, most of the carriers on the metal side still remain unchanged to such a state that they can exceed the Schottky barrier. Thus, even when the electric field is applied, the current based on the transportation of the carriers from the metal side to the semiconductor side remains unchanged in a short-circuited state and is approximately constant at a very low value (backward characteristic). Thus, the Schottky junction having the Schottky barrier normally has rectification that allows only the transportation of the carriers from the semiconductor side to the metal side. One that has utilized this rectifying action corresponds to the Schottky barrier diode.
It is understood from the above that the forward characteristics of the Schottky barrier diode are determined depending on the behavior of the majority carrier on the semiconductor side. Thus, the Schottky barrier diode has the feature that as compared with the normal pn-junction diode that utilizes the injection of a minority carrier, a voltage drop in the forward direction is small and switching to a high frequency is fast. The height of a Schottky barrier at a normal Schottky junction is lower than a diffusion potential at a pn junction. Thus, the Schottky barrier diode has the feature that the voltage at the rising edge of a current at the forward characteristics of the Schottky barrier diode is lower than at the pn junction diode. From these characteristics, the Schottky barrier diode is applied to such a driver that a high-speed switching operation at a high frequency/low-voltage is desired, as in the LCD driver starting with a standard logic IC, a power circuit for audio equipment, a switching power supply and the like.
A latch-up preventing circuit has heretofore been configured by a Schottky barrier diode manufactured as a discrete product and mounted onto its corresponding LCD driver in external form. On the other hand, according to the discussions of the present inventors et al., there have been demands or the like for a small size-chip solution of the LCD driver per se and its reduction in power consumption as trends in demand with a rapid increase in the mounting to a mobile communication terminal or the like. A technique for building the Schottky barrier diode in its corresponding LCD driver has been invented. It has been desired to realize an LCD driver brought into low power consumption in space-saving form at low cost by building a Schottky barrier diode into a chip for forming an LCD driver in particular.
A structure and manufacturing process or the like of a Schottky barrier diode formed over a semiconductor substrate have been disclosed in, for example, Japanese Unexamined Patent Publication No. 2006-310791 (patent document 1), Japanese Unexamined Patent Publication No. Hei 10 (1998)-117002 (patent document 2) or Japanese Unexamined Patent Publication No. Hei 8 (1996)-64845 (patent document 3) or the like.